Additive manufacturing techniques and processes generally involve the buildup of one or more materials, e.g., layering, to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods, in which material is removed. Though “additive manufacturing” is an industry standard term (ASTM F2792), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including, e.g., freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing techniques may be used to fabricate simple or complex components from a wide variety of materials. For example, a freestanding object may be fabricated from a computer-aided design (CAD) model.
A particular type of additive manufacturing is commonly known as 3D printing. One such process, commonly referred to as Fused Deposition Modeling (FDM), or Fused Layer Modeling (FLM), comprises melting a thin layer of thermoplastic material, and applying this material in layers to produce a final part. This is commonly accomplished by passing a continuous, thin filament of thermoplastic material through a heated nozzle, or by passing thermoplastic material into an extruder, with an attached nozzle, which melts the thermoplastic material and applies it to the structure being printed, building up the structure. The heated material is applied to the existing structure in layers, melting and fusing with the existing material to produce a solid finished part.
There are two different approaches commonly used to produce large parts during additive manufacturing. In the first approach, material is deposited through a nozzle vertically downward onto a worktable to print the first layer. Subsequent layers are deposited over a contour of the first layer to produce a final, solid finished part. In this first approach, the nozzle is moved along a horizontal plane to trace the geometry of each layer. The worktable may move downward away from the nozzle after each layer is completed to provide clearance for the next layer. In some aspects, the nozzle may be able to move vertically upward away from the worktable in addition to having a moveable worktable. If the nozzle is vertically displaceable, the worktable may not need to move each time a layer is completed, or may need to move less.
The second approach to producing large parts during additive manufacturing is to utilize a nozzle that moves in a horizontal plane as well as in a vertical plane. In this arrangement, the nozzle may move downward towards a fixed worktable, may move around the worktable to trace the geometry of the printed layer, and may then move upward away from the worktable to provide clearance for the next layer.
Both of these approaches generally use a method that is different than traditional net shape 3D printing. In net shape 3D printing, flowable, thermoplastic material is added in thin horizontal layers, with each new layer being fused to the material already deposited to build a final part shape layer by layer. If the layers are thin and dimensionally accurate enough, a final net part shape results, which has the advantage that no additional machining or trimming is required. A disadvantage is that, because the layers are thin, many layers are required to build the part, so the process requires a significant amount of time to perform, especially on large parts. It is desirable, therefore, to reduce the time needed to perform this process, which may also decrease manufacturing costs.
The approach widely used for manufacturing large parts using 3D printing, commonly referred to as near net shape, is to deposit material in thicker layers (compared to net shape 3D printing), which yields a final part that is slightly larger than the final net shape desired, and then to machine the part to the final net size and shape. The advantage is that it is substantially faster than the thin layer approach. However, a mechanism, or a machine, to perform the trimming or machining operations is required to achieve the final net size and shape.
In the first 3D printing approach, with the downward moving worktable, parts are generally printed on one machine and trimmed on a separate machine. The requirement that vertical motion be accomplished by moving the sometimes large worktable makes trimming, using this moving worktable approach, impractical for machining operations.
During operation using the second approach, with a fixed worktable and moving nozzle, both printing and trimming can be performed on the same machine by providing mechanisms to move the print head and the trimming head independently of each other over the same worktable. While the trimming mechanism is off the worktable, the part is printed using the printing mechanism. Once the printing is completed, the printing mechanism moves off the worktable. Subsequently, once the printing mechanism is moved off the worktable, the trimming mechanism is used to machine and trim the printed part to the final net size and shape. In this approach, the worktable is fixed, and the printing and trimming mechanisms maneuver over the worktable.
One way to configure a machine to operate in this manner is to position the worktable in the center located near the floor and to position two walls on either side of the worktable. The top edge of the walls support linear trackways with two gantry structures that span between the walls and move on the trackways. One gantry is equipped with the printing mechanism, and the second gantry is equipped with the trimming mechanism. With this configuration, a part, up to the overall size of the worktable, can be printed using the print gantry, and then the part can be machined or trimmed to size to form a solid finished part using the trimming gantry.
In the practice of the aforementioned processes, some major disadvantages have been encountered. Both of the described printing approaches—either using a fixed or a movable worktable—share a common limitation. In each of the two described printing approaches, the maximum height of the part that can be printed is determined by the maximum number of layers that can be printed, which is limited by the height of the machine. In other words, in both approaches, the height of the part is limited to the height of a computer numeric control (CNC) machine. In order to produce long parts, tall machines are required, which is impractical due to general machine structure limitations and building ceiling height limitations.